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CandeCAD Pro
CandeCAD Pro has revolutionised finite element
technology in the AutoCAD environment.
For the first time ever, advanced finite element technology
can be used on a routine basis for culvert and pipe
analysis, design and evaluation. More importantly, this
technology is now available to everybody with some engineering
background, even if you are not an expert in finite
element analysis.
CandeCAD Pro will result in significant savings in time
and money while ensuring better engineered, safer and
more economical designs
[Culvert ANalysis
and DEsign inside autoCAD]
Introduction
Overview
of CandeCAD Pro
Finite Element Routine
Description of CANDE
Element Description and Material
Models
Program Output
Selected References
Introduction
CandeCAD Pro (Culvert ANalysis and DEsign inside AutoCAD)
is a two-dimensional nonlinear finite element buried
pipe and culvert software application used for the structural
design, analysis and evaluation of buried pipes, culverts
and other soil-structure interaction systems. CandeCAD Pro
incorporates built-in linear and nonlinear soil material
models and pipe and culvert material models to analyse
almost any installation condition. Typical buried structures
currently supported by CandeCAD Pro include:
· corrugated metal pipes and culverts,
· corrugated aluminium pipes and culverts,
· plain wall and stiffened steel pipes,
· reinforced concrete pipes, box culverts and
arch culverts,
· plastic pipes and culverts.
Soil-structure interaction is correctly modelled by
incorporating built-in nonlinear soil, pipe and culvert
material models and incremental construction procedure
(i.e., incremental placement of backfill materials).
This ensures that the actual or expected construction
procedures are closely modelled by the software.
The software was developed with two main objectives
in mind:
1) to make it the fastest and easiest to use finite
element buried pipe and culvert analysis software in
the world, and
2) to empower our users to incorporate advanced modeling
and analysis techniques in their design environment
leading to better engineered, safer and more economical
designs for pipelines and culverts.
The source code of one of the world’s most widely
used and tested buried pipe and culvert software applications
CANDE has been incorporated into CandeCAD Pro because of
its proven track record over the past 25 years and its
familiarity amongst its users worldwide. Contact candecad@ssismint.com
for more information and technical assistance.
CandeCAD Pro
Overview
CandeCAD Pro is the fastest, most flexible and easiest to
use finite element buried culvert and pipe analysis
software in the world. Ease and speed of use are ensured
through many built-in mesh generation features and a
powerful graphical user interface. CandeCAD Pro supports
many different culvert and pipe materials such as reinforced
concrete, steel, aluminium, plastic and a basic model
for other culvert and pipe materials. User selectable
and easy to use built-in linear and non-linear soil
material models are available to represent in situ and
structural backfilling materials.
CandeCAD Pro provides the user with never seen before graphical
ability to generate finite element meshes simply and
quickly all in the familiar AutoCAD® environment.
The user is allowed to make use of all the built-in
AutoCAD® drawing tools in addition to the many new
CandeCAD Pro commands. The result is superior speed, ease
of use and productivity. Once the finite element mesh
is created, the user can assign material models and
construction increment numbers to the mesh elements
by simply selecting the elements graphically using a
mouse and clicking on the appropriate CandeCAD Pro command
buttons. Display windows and drop-down lists are available
to navigate the user through the simple process of assigning
material models, boundary conditions, external loads,
pressures etc.
CandeCAD Pro User Interface - click
to veiw enlargement
Input file generation is automated by a simple click
of a button and even includes basic error checking routines.
The user is warned of errors in the mesh and shown where
these errors are (if any). Another first for CandeCAD Pro
is super fast importing of program output. Graphing
flexibility gives the user full control over output
graphics. Automatically generated graphs can be copied
or exported to standard drawing files, software packages
or used with AutoCAD to create professionally looking
engineering drawings.
Finite Element Routine
CandeCAD Pro incorporates the widely used and accepted finite
element source code of CANDE developed under sponsorship
of the United States Federal Highway Administration
(FHWA). The trusted and well calibrated source code
of CANDE makes it the obvious choice for use in CandeCAD Pro.
CANDE Description
CANDE was originally developed under sponsorship of
the U.S. Federal Highway Administration (FHWA) in 1976
(Katona et al., 1976). Since CANDE’s first introduction
in the market in 1976, it has seen numerous updates
over the past 25 years under the sponsorship of the
FHWA. It has gained substantial market acceptance in
the United States, Canada, Europe, Australia and Africa.
CANDE was last updated in 1989 (Musser, 1989) and it
operates in the now obsolete DOS® environment. CANDE
effectively models soil-structure interaction by various
means such as incremental construction, interface slip,
hyperbolic stress-strain relationships for soil, and
simulation of compaction pressures. The program has
been used successfully in the past to model regular
and large-span culverts and buried pipe installations
by various researchers and design consultants such as:
· Chang et al. (1980)
· McVay and Selig (1982)
· Katona et al. (1979)
· Vaslestad (1990)
· McGrath et al. (1999)
· Webb (1999)
· Selig and McGrath (1994)
· Oswald and Furlong (1993) and many others.
CANDE is a two-dimensional plain-strain finite element
computer program dedicated to the design and analysis
of buried culverts and pipes. The program has two execution
modes, one for design and one for analysis. Design requires
specifying geometry, loading conditions, and material
properties without specifying culvert and pipe wall
section properties such as wall area, moment of inertia
and section modulus. Desired safety factors against
failure limit states are required for this mode and
the program will solve the design problem through a
search and analysis routine. The analysis mode on the
other hand requires specifying culvert and pipe wall
section properties only, and the program will predict
the structural performance of the culvert or pipe together
with factors of safety against possible modes of failure.
Technical Description
The culvert-soil structure is constructed of continuum
quadrilateral and triangular soil elements, beam-column
elements, and interface elements. The soil elements
consist of either 3 or 4 external nodes with two translational
degrees of freedom at each node (vertical and horizontal
displacements) in addition to internal degrees of freedom.
Various soil models are available for representing stress-strain
behaviour of the soil elements from linear elastic to
nonlinear stress-dependent. The beam-column elements
are bi-nodal with three degrees of freedom at each node,
two translational and one rotational. Various models
are available to represent different culvert and pipe
material such as corrugated metal, reinforced concrete,
plastic, and a basic model for nonstandard materials
or built-up pipe materials. The models include nonlinear
material behaviour such as metal yielding and concrete
cracking and crushing. Interface elements are used to
model the interface between two subsystems such as the
culvert wall and the surrounding soil, or the trench
wall and trench fill. These elements allow for frictional
sliding (interface shear force exceeds the product of
normal force and friction coefficient), separation (interface
normal force exceeds the tensile breaking limit), and
re-bonding if additional loading brings the subsystem
together again. The interface elements consist of three
nodes located at the same position initially while one
interior node is used to represent the interface and
the two outside nodes are used to represent the subsystems.
Example of CandeCAD Pro FE Mesh - click
for enlarged view
Program Output
Structural responses for the beam-column elements such
as bending moment, thrust, shear, normal pressure, shear
pressure and displacement are imported and displayed
by a simple click of a button. Similarly, vertical and
horizontal soil stresses and strains in the in situ
and backfill materials can also be presented graphically.
Horizontal Soil Stresses - click
for enlarged view
Incremental Deflections - click
for enlarged view
Bending Moments - click
for enlarged view
Selected References
Chang, C.S., Espinoza, J.M., and Selig, E.T., “Computer
Analysis of Newtown Creek Culvert”, Journal of
Geotechnical Engineering, ASCE, Vol. 106, No. GT5, May
1980, pp. 531-556.
Katona, M.G., Meinhert, D.F., Orillac, R., and Lee,
C.H., “Structural Evaluation of New Concepts for
Long-Span Culverts and Culvert Installations”,
Report No. FHWA-RD-79-115, Federal Highway Administration,
Washington, D.C., 1979.
Katona, M.G., Smith, J.M., Odello, R.S. and Allgood,
J.R., “CANDE - A Modern Approach for the Structural
Design and Analysis of Buried Culverts”, Report
No. FHWA-RD-77-5, U.S. Naval Civil Engineering Lab,
Port Hueneme, CA, October 1976.
Mc Vay, M.C., and Selig, E.T., “Performance and
Analysis of a Long-Span Culvert”, Transportation
Research Record 878, TRB, National Research Council,
Washington, D.C., 1982, pp. 23-28.
McGrath, T.J., Selig, E.T., Webb, M.C., and Zoladz,
G.V., “Pipe Interacton with the Backfill Envelope”,
Report FHWA-RD-98-191, Federal Highway Administration,
Washington, D.C., June 1999.
Musser, S.C., “CANDE-89 User Manual”, Report
No. FHWA-RD-89-169, Federal Highway Administration,
June 1989.
Oswald, C.S., and Furlong, R.W., “Observed Behavior
of a Concrete Arch Culvert”, Report No. TX- 93+932-1F,
Center for Transportation Research, University of Texas
at Austin, Austin, Texas, February, 1993.
Selig, E.T., and McGrath, T.J., “Investigation
of Structural Behavior of 36-ft Span Con/Span Bridge”,
Report Prepared for Con/Span Bridge Systems, Inc., Dayton,
Ohio, Department of Civil Engineering, University of
Massachusetts at Amherst, December 1994.
Vaslestad, J., “Soil Structure Interaction of
Buried Culverts”, Ph.D. Dissertation, Department
of Civil Engineering, Norwegian Institute of Technology,
1990.
Webb, M.C., “Improved Design and Construction
of Large-Span Culverts”, Geotechnical Report No.
NCH98-458D, Ph.D. Dissertation, Department of Civil
and Environmental Engineering, University of Massachusetts
at Amherst, MA, USA, February 1999.
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